There are a variety of pathological conditions which require surgical intervention in and around the spinal epidural space. The most common of these is intervertebral disc herniation. Other conditions which require surgical intervention in and around the epidural space include, but are not limited to, foramenal stenosis, tumor excision procedures including excision of neurofibromas, meningiomas, and the like, and procedures involving nerve root blocks.
The neural foramen provides an entry port into the epidural space. The foramen is circumscribed by the pedicles of adjacent vertebral bodies and the floor of the foramen is formed from the annulus of a disc positioned between adjacent vertebra. Disc herniations extend from the anterior surface of the epidural space, extending into the space or out of the neural foramen. There are currently three major routes for accessing herniated disc tissue: laminectomy and hemilaminectomy procedures, anterior approaches and posterolateral approaches.
Laminectomy and hemilaminectomy procedures are some of the more common procedures for treating herniated discs. These procedures allow direct access to the epidural space through the removal of all, or a portion, of the adjacent lamina (i.e. the posterior vertebral surface) to expose the nerve root and the disc herniation. These procedures are tedious and involve extensive dissection and surgical manipulation associated with the required bone excision. An added complication of these procedures is the threat of spinal instability resulting from excess bone removal.
In the posterolateral approach for accessing herniated disc tissue, exemplified by U.S. Pat. No. 4,573,448 to Kambin, the patient is positioned in a lateral decubitus or in a prone position. In this method, instruments are introduced into disc tissue at an angle of approximately 35.degree. relative to the mid-sagittal plane of the patient (the longitudinal plane running perpendicular to the spine). Here, attempts are made to indirectly access the herniated tissue by entering disc tissue and excavating to the site of the herniation. Entry is complete when the surgical tools are positioned within the disc tissue anterior to the spinal epidural space. Once in position, the surgeon excavates through the disc tissue, at approximately a 60.degree. angle, posteriorly, to the site of the herniation and removes the herniation from inside the disc, without entering the epidural space.
The Kambin procedure can be performed using one or two incision sites and requires steerable tools and angulated scopes. Because the method necessarily involves excavation of the disc tissue, there is significant motivation to keep the excavation as narrow as possible. The narrow opening requires successive entry and removal of endoscopic equipment and excavators thereby increasing the length of time of the surgical procedure. Normal disc tissue is destroyed and removed in this technique with the added complication that the surgeon cannot simultaneously view the area to be excised while excavation is taking place. The surgeon is also unable to see into the epidural space where the actual pathology lies unless a second incision on the opposite side of the spine is used, thereby permitting simultaneous visualization and excision of disc tissue.
U.S. Pat. No. 4,638,799 to Moore details a needle guide apparatus for positioning surgical instruments suitable for disc chemonucleolysis via a posterolateral approach. Like Kambin, Moore also contemplates indirect entry disc tissue to correct a disc defect. The needle guide fixes the angle of entry into disc tissue with preferred entry angles ranging from 45.degree. to 55.degree.. Neither Kambin nor Moore discloses a method for entering the spinal epidural space.
Anterior approaches to correct intervertebral disc herniation are generally an improvement over the posterolateral approach because the target herniation is in line with the entry port. As a result, the herniation is easier to visualize from within the disc tissue. However, anterior approaches typically require extensive insufflation of the peritoneal space. Where insufflation is not employed, entry into the peritoneum is complicated by the inherent risk that bowel or ureter tissue could be injured and such injury to the bowel can result in life threatening sequelae. Like the Kambin approach described above, the anterior approach also requires that the surgeon remove intact, normal disc tissue to get to the area of the herniation while the surgeon works from inside the disc space and the anterior approach does not permit direct visualization of the epidural space where the pathology lies. Therefore there remains a need in the medical arts for a surgical method and device which permits direct access and visualization of the epidural space without requiring extensive removal of bone or disc tissue.
In the aforementioned methods, there is the potential for complications resulting from the length surgery, patient recovery time and the risk of complications during the surgical procedure. Patient recovery time is further extended when the patient is of an advanced age. Since disc herniation is a degenerative pathology, it is not unexpected that the majority of individuals with disc herniations or other back complications requiring access to the foramenal space are of advanced age. For elderly patients, increased surgical time, general anesthesia and spine destabilization resulting from bone removal can all increase patient recovery time. Thus, there is a need for a surgical method that decreasing the length of surgery and reduces the length of patient recovery.